Here we develop novel in situ and circulating nanoscale sensing technologies heretofore unavailable to directly measure the cumulative fluid-structure forces experienced by blood platelets during circulation. Elevated shear is responsible for the myriad of adverse events in implantable cardiovascular devices including thrombosis and bleeding. We propose to utilize mechanosensors made using DNA nanotechnology to quantify physical force perturbations experienced by circulating cells as they traverse high shear flow paths. By creating and characterizing this new assay tools system, this work has potential to improve and enhance the safety and efficacy of cardiovascular therapeutic devices. This resubmission has been updated based on helpful feedback. At the nanoscale, pushing, pulling, and shearing forces drive biochemical beneficial processes in development and remodeling, but also pathological processes in disease progression. In blood platelets, shear activation as experienced in a ventricular assist device or in stenotic atherosclerotic artery leads to an increased likelihood of thrombosis, but without a tool to measure the shear dose, i.e. intensity x time, that a given circulation will impart, our capability to develop therapeutic interventions is limited. Nanoscale sensor modules would allow us to ask not only how platelet loads affects thrombotic potential, but also to predict how implantable devices in conjunction with specific vasculature will affect potential for stroke or other thromboembolic events, and ultimately inform future designs for enhanced hemocompatibility. In a high-risk, high-reward collaboration involving bioengineers and physicians, we propose to apply the DNA origami approach to create two varieties of fluorescent and tunable bistable nanosensors: one that is sensitive to shear loading (surface parallel) and another that is sensitive to compressive loading (surface perpendicular). We will decorate micron-scale polymer microbeads as well as human blood platelets with these sensors, and using microfluidic platforms, we will tune the mechanics of these sensor-on-particle systems, including their linkages, to maximize their sensitivity to both shear and impact. The molecular precision and programmability of DNA-based mechanosensors can enable highly parallel measurements with tunable sensitivity to forces as small at tens of femtonewtons. This interdisciplinary field has historically been driven by the development of technologies for precise application and measurement of cellular and molecular forces; each new tool has enabled vast new lines of inquiry, and with this proposed work, DNA- based nanotechnologies can lead to another transformation in the field of cardiovascular mechanobiology. Success in this endeavor will result in the creation of novel tools for measuring the cumulative shear and compressive loading that circulating cells experience as they move through high shear microenvironments. Insights from such measurements will enable the development of improved implantable devices, pharmacologic agents to mitigate shear effects and new lines of inquiry for improving our understanding of the role of shear and compressive loading in platelet activation.